This is a psychophysical investigation of the mechanisms of spatial pattern vision in adult, human observers with normal vision. Both detection and discrimination performance are examined. The goals of the research are (1) to expand present information about the bandwidths of psychophysically defined tuned pathways or channels with respect to orientation, spatial frequency, and phase; (2) to determine whether visual discrimination is more closely related to spatial frequency or periodicity, to phase or location; (3) to compare the effects of masking on discrimination with its effects on detection; (4) to compare central and peripheral vision with respect to the relationship between detection and discrimination performance, bandwidths of individual pathways, and the effects of masking; (5) to develop psychophysical models of detection and discrimination. All measures will be taken at photopic levels of illumination. A modified forced choice procedure will be used which gathers simultaneous detection and discrimination data.